Trans-acting small interfering RNAs (tasiRNAs) are unique to plants. They are the products of TAS genes, but they function to regulate other genes (thus the name “trans-acting”). The production of tasiRNAs requires miRNAs, which bind to and ultimately lead to cleavage of the primary TAS transcript. TAS3 is the best studied TAS gene. Its production depends on miR390, and its tasiRNA products target AUXIN RESPONSIVE FACTOR (ARF) genes. Xia et al. characterized genes corresponding to the miR390-TAS3-ARF pathway in thousands of plant species to uncover their evolutionary trajectories. Their data “illuminate the evolutionary path of the miR390-TAS3-ARF pathway in land plants, and demonstrate the significant variation that occurs in this functionally important and archetypal regulatory circuit.” Plant Cell 10.​1105/​tpc.​17.​00185